The present invention relates to the medical field, more particularly to cardiac defibrillation, and particular to external or transthoracic defibrillation and internal defibrillation, as well as the implantable defibrillator, and has for its object new impulses or series of defibrillation impulses, as well as a device to generate or produce these latter.
At present, the great majority of defibrillations are carried out by means of a positive monophase impulse resulting generally in the discharge of a capacitor through the patient and, as the case may be, an inductance.
However, numerous forms of impulses are possible (see for example: A. Cansell, La Revue des Samu; 1997-5, 229 to 237).
It has been particularly proposed recently to interrupt the discharge of the capacitor, then to modify the connection to end the discharge with a reversed polarity, so as to supply impulses in the form of a biphase wave.
This manner of biphase defibrillation has been described in numerous works, particularly for example in the document WO 95/05215. The same principle of biphase defibrillation (with two or more phases of opposite polarity) is however older, because the first defibrillations were carried out by Prevost and Batelli by means of a sinusoidal AC current of 45 Hz (CR Acad. Sci. 1899; 129:1267). Similarly, all the defibrillations used in the former USSR used and still use an oscillating capacitor discharge, comprising two to three alternate phases (Negovsky et al., Resuscitation 1980; 8:53-67).
Moreover, it has also been proposed to use, to excite the cardiac cells, series of rectangular impulses of the same polarity delivered at high frequency and delimited by a monophase rectangular envelope, so as to obtain a pulsed monophase wave of rectangular form and chopped by a high frequency signal (Janice L. Jones et al., xe2x80x9cCellular excitation with high-frequency chopped defibrillator waveformsxe2x80x9d, Proc. IEEE, p. 17 et 18, 6/1994).
However, these different types of known defibrillation impulses all have, either because of their nature, or because of the mode of embodying the devices generating them, limitations and drawbacks such as for example limited available energy, great difficulty of practical embodiment, limited efficiency for a given available energy or else a risk of harm to the patient.
Moreover, there continuously exists the need, given their critical character, of improving the efficiency of defibrillation techniques, particularly to reduce the quantity of energy delivered by them to the patient whilst guaranteeing a success rate greater than that obtained by present techniques.
The present invention particularly has for its object to overcome certain of the drawbacks and limitations mentioned above and to fulfill the mentioned need.
However, the inventors have determined, in a surprising and unforeseeable manner, that the impulses or series of defibrillation impulses constituted by a wave with at least two phases whose successive phases of opposite polarity are cut or chopped at a higher frequency than the frequency of said successive phases, will permit overcoming at least certain of the drawbacks and limitations mentioned above and will have a defibrillation efficiency substantially greater than the existing shapes of defibrillation waves.